|Roth RH: The Straight-Wire Appliance 17 years later. J Clin Orthod 1987 Sept;21(9):632-42.
McGann abstract: the Roth prescription
Dr. Roth started by saying that he uses the official “true” Straight Wire Appliance, having received the first case in 1970 and then changing his practice fully by 1973. The manufacturers enhanced the product in many ways, but causing confusion in those early years by the different claims. He believes that orthodontists knew more about straight wire in 1973 than when the article was written 4 years later. At that time, he claims that the orthodontists perceived no difference in preadjusted appliances and the true SWA.
Next he discussed the Andrews extraction bracket series to compensate for tipping and rotation when closing extraction space. The original straight wire brackets, according to Roth, were designed to treat only non-extraction cases with ANB less than 5 degrees. The 11 other SWA sets were designed for extraction cases, different ANB, and anchorage requirements. Inventory was becoming a problem, especially since Roth did not use bonded appliances then, ONLY bands! Because of this, Roth worked on a prescription that would be applicable to most cases.
The Roth prescription, introduced in 1976, came out of the problems that Roth saw in the original straight wire appliance, mainly the need to place compensating and reverse curves in the upper and lower arches. He also noticed that anchorage was a problem in some cases as the mesial inclination allowed the molars to drift mesial [into the extraction space]. Roth did NOT translate teeth, and did not feel that sliding teeth along a rectangular wire was efficient anyway due to friction. He did not like tipping teeth and then uprighting. He also wanted to over-correct and then let the teeth settle into the final position. He wanted to fill the slots with a full size archwire (22x28) while Andrews used the maximum size 18x25. Roth reasoned that if the archwire was firmly tied into the bracket slot then it would remain there no matter how far the tooth was moved (as in I do not need all those extra brackets).
Several years of clinical evaluation led to the conclusion that he could treat the majority of cases with a single prescription with over-correction in all planes of space to meet the 6 Keys of Andrews. He did this will full size archwires, rarely placing offset bends, with the archwires being flat to level the curve of spee. Positioning was more incisal on the anterior teeth than recommended by Andrews to accomplish this (same idea as in McGann positioning of the IP Appliance). Hooks were added for the use of short class II and III elastics. [note: there were hooks on the mesial of the upper bicuspids and distal of the lower bicuspids on the original Roth appliances, just as with the IP Appliance).
Roth added 5 degrees of extra torque to the upper central incisors than the Andrews standard, and to coincide, less negative torque in the upper cuspids. There was a 2 degree mesial rotation and an extra 2 degrees of distal root tip since most of the cuspids were being retracted.
Multiple torque? Yes, Roth made a separate set of “super” torque upper anterior brackets for class II, division 2 cases. 14 degrees of distal offset was built into the upper molar tubes, much more than the Andrews normals.
For upper 4 extraction cases, upper molar tubes with zero degree torque (IP Appliance “D” variation) and high torque brackets (Li in IP terminology) were used to compensate for “half a molar is smaller than a full bicuspid”.
In the lower arch, the lower incisor and canine torque was the same as orthodontic norms of Andrews with some distal rotation throughout the posterior segments since the teeth settle more mesial than the uppers.
Roth then developed the “Tru-Arch Form” archwire (expanded for most cases) that helped the over-correction concept. The idea of the archform affecting the rotational position of teeth was made (similar to IP Appliance rotation diagnosis). The most prominent point was the 4s, the widest point the mesial-buccal cusp tips of the first molars (then tapering in).
According to Roth and also an article by Lee and Lundeen, mandibular movement requires a broad archform across the anterior teeth. 73% of the population would require a broad archform, and only 14% the commonly used orthodontic narrow anterior archform. If the archform in the lower is too narrow, then the result is “over-coupling” of the anterior teeth or improper anterior guidance (nice term for loss of anterior overjet?).
There is a lot of over-correction in the appliance, illustrated by the roots of extracted teeth on a full size archwire (the roots were not all parallel with the Roth prescription as they were with the SWA). According to Roth, this is what it takes to get the teeth into the desired positions, and the over-correction will never be express in the mouth since:
Slot and archwire inefficiency
the wire becomes passive, dropping the force to a level not capable in moving the teeth, so the full prescription will not be expressed.
Teeth relapse to original positions
build compensations in the brackets for unwanted tooth movements (mechanics)
Roth says that the chairtime of the doctor is 1/5th what it was when bands were being used to hold the preangulated appliances and bending rectangular wire as the norm. Non extraction cases could be treated in 6-12 months, other cases dropping by 3-6 months compared to before.
Advantages of SWA
Does not diagnose and treatment plan cases, but it will detail tooth positions better, more consistently, and faster than bending archwires. The brackets must be repositioned if they are not set correctly. Stability has been reported as excellent after 17 years experience.